错误获取财产“行”在GridView

Question

我在这是在注释中显示的代码得到错误（请仔细阅读）

<script type="text/javascript" src="http://code.jquery.com/jquery- 2.2.1.min.js"></script> 
<script type="text/javascript"> 
    var grid = document.getElementById("<%=gvCustomers.ClientID%>");//gvCustomers is the ID of a gridview 
     val();  
    function val() { 
     if (grid.rows.length > 0) {//Unable to get property 'rows' of null or 'undefined' value 
      alert(grid.rows.length); 
     } 
    } 
</script> 

我要去哪里错了？即使我没有空的gridview！

的HTML代码也在这里：

<form id="form1" runat="server"> 
    <div> 
<asp:GridView ID="gvCustomers" runat="server" AutoGenerateColumns="false" ShowHeaderWhenEmpty ="true" 
    DataKeyNames="CustomerID" OnRowDataBound="OnRowDataBound"> 
    <Columns> 
     <asp:TemplateField> 
      <ItemTemplate> 
       <asp:Button ID ="btn" Text ="+" runat="server" /> 
       <asp:Panel ID="pnlOrders" runat="server" Style="display: none"> 
        <asp:GridView ID="gvOrders" runat="server" AutoGenerateColumns="false" CssClass = "ChildGrid"> 
         <Columns> 
          <asp:BoundField ItemStyle-Width="150px" DataField="OrderId" HeaderText="Order Id" /> 
          <asp:BoundField ItemStyle-Width="150px" DataField="OrderDate" HeaderText="Date" /> 
         </Columns> 
        </asp:GridView> 
       </asp:Panel> 
      </ItemTemplate> 
     </asp:TemplateField> 
     <asp:BoundField ItemStyle-Width="150px" DataField="ContactName" HeaderText="Contact Name" /> 
     <asp:BoundField ItemStyle-Width="150px" DataField="City" HeaderText="City" /> 
    </Columns> 
</asp:GridView> 
     </div> 
</form> 

Answer 1

你没有选择权的gridview的。

试试这个

var grid = document.getElementById("gvCustomers"); 

UPDATE

使用jQuery，试试这个：

$(document).ready(function(){ 
var grid = document.getElementById("gvCustomers"); 
    function val() { 
     if (grid.rows.length > 0) {//Unable to get property 'rows' of null or 'undefined' value 
      alert(grid.rows.length); 
     } 
    } 
    val(); 
});